1. Field of the Invention
The present invention relates to a liquid crystal display cell and a manufacturing method thereof, and more particularly to a liquid crystal display cell and a manufacturing method thereof capable of improving the visual angle.
2. Description of the Related Art
In a liquid crystal display cell or liquid crystal cell utilized for a liquid crystal display, a particular orientation state of liquid crystal molecules is changed to a different state by some external action as electric field. The change in the optical property caused by the change of orientation of the liquid crystal molecules is utilized as a visual change in a display. Usually, for orientating liquid crystal molecules in a particular state, the surface of the glass substrates which sandwich a liquid crystal layer are subjected to orientation treatment.
In a conventional liquid crystal cell of twisted nematic (TN) type, the orientation treatment is achieved by rubbing a pair of glass substrates (having electrodes, an orientation layer, and the like on its surface,) which sandwich a liquid crystal layer with a cotton cloth or the like in one direction, i.e. a so-called rubbing treatment.
When rubbing treatment is done to substrates, the direction of rubbing is arranged in such a way that the rubbing directions of the upper and lower substrates are orthogonal to each other. When the liquid crystal cell is of negative display type, parallel polarizers are disposed in such a way that one of the rubbing directions is parallel to the polarization axis of a neighboring polarizer. In the case of positive display, crossed polarizers are disposed in such a way that polarization axes are parallel to the rubbing directions of neighboring substrates.
When orientation treatment is done by rubbing as described above, orientated direction of the liquid crystal molecules become uniform on the substrate surface. Thus, when the display is viewed by an observer, there occurs a visual angle dependency of display, that the display can easily be observed only from a certain limited range of observation. Reference can be made on the visual angle dependency of display to the U.S. patent applications Ser.No. 08/115,441 filed on Sep. 1, 1993, Ser. No. 08/191,554 filed on Feb. 4, 1994, and Ser. No. 08/191,636 filed on Feb. 4, 1994.
Further, rubbing may generate electrostatic charge, which may cause dielectric breakdown of the orientation film, or insufficient orientation of liquid crystal molecules thereat, and hence, a display defect. In a liquid crystal cell employing active (drive) matrix, electrostatic charge generated by rubbing may cause breakage of drive elements or wirings formed thereon.
Yet further, a vast amount of fine particles generated by rubbing treatment may attach to the substrates by electrostatic force and may become the cause of inaccurate gap of the liquid crystal cell and/or of display defects as black points and white points.